The primary objectives of this research are to measure zinc retention and to quantify total body zinc losses in mature, healthy women during the last trimester of pregnancy; to evaluate the effect of changes in dietary zinc and protein on zinc utilization; and to establish norms for biochemical measures of zinc status in pregnant women on known, constant and nutritionally adequate dietary intakes. The levels of zinc and protein intake will be equal to current NRC and WHO recommendations for pregnancy. The data will provide a basis for development of new recommendations if the current premises are not upheld. Zinc retention will be quantified by total zinc balance studies carried out in a metabolic unit. Routes of zinc loss to be measured are feces, urine, skin, vaginal secretions, hair and nails. A stable isotope of zinc--70zn--will be fed to evaluate absorption and endogenous fecal zinc losses. Nitrogen, calcium, phosphorus, sodium, potassium, iron and copper balances will also be measured. As dietary calcium will be fed at constant levels throughout the investigation and examination of the effect of changes in dietary protein and zinc on calcium balance will be possible. Measurements of zinc levels in the blood, saliva and hair will provide a baseline for comparison of these parameters in other pregnant women.